perf(core): cache port discovery for step invocations

[joeyhotz]

Description

Reuse the process-level getPortLazy() cache from #2522 for self-hosted step invocations. The step handler currently calls getPort() for every step; in a production burst profile, process.report.getReport() beneath that lookup accounted for 83% of peak wall samples.

This is safe because the listening port is stable for the process lifetime, only concrete ports are cached, concurrent first calls are deduplicated, and undefined results retry. The existing Vercel branch still skips discovery.

How did you test your changes?

• Added a regression test proving two step invocations share one port lookup.
• pnpm --filter @workflow/core test (1,483 passed; 3 expected failures)
• pnpm --filter @workflow/core typecheck
• pnpm turbo build --filter='@workflow/core...'
• Biome check on the changed TypeScript files

PR Checklist - Required to merge

• 📦 pnpm changeset was run to create a changelog for this PR
  • correct bump (patch for bug fixes, minor for new features, major for breaking changes)
  • only changed packages included
• 🔒 DCO sign-off passes (run git commit --signoff)
• 📝 Ping @vercel/workflow in a comment once PR ready and checklist complete

[changeset-bot]

🦋 Changeset detected

Latest commit: f4e31ad

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 16 packages

Name	Type
@workflow/core	Patch
@workflow/builders	Patch
@workflow/cli	Patch
@workflow/next	Patch
@workflow/nitro	Patch
@workflow/vitest	Patch
@workflow/web-shared	Patch
@workflow/web	Patch
workflow	Patch
@workflow/world-testing	Patch
@workflow/astro	Patch
@workflow/nest	Patch
@workflow/nuxt	Patch
@workflow/rollup	Patch
@workflow/sveltekit	Patch
@workflow/vite	Patch

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[joeyhotz]

@vercel/workflow

[vercel]

@joeyhotz is attempting to deploy a commit to the Vercel Labs Team on Vercel.

A member of the Team first needs to authorize it.

[joeyhotz]

Wow guys I'm testing this with a patch, I'm getting huge performance improvements for burst tests I'm doing. Before it was causing requests to not be served (I assume hogged too much of the event loop), but now it doesn't cause requests to not be served, and also goes through the queue looooads faster.

[VaguelySerious]

Great catch!

[github-actions]

Backport PR opened against stable: #2997. Merge conflicts were resolved by AI — please review carefully. (backport job run)

[joeyhotz]

@VaguelySerious hope it's okay to ask a question, as you know I got a few PRs through recently into the v5 beta, are the beta versions generally stable and usable in production? Or should I avoid? When something gets merged into main, does it instantly increment a version and useable? Honestly these are my first sets of OSS contributions.

[VaguelySerious]

@joeyhotz Anything landing on main will be in a beta release within ~1 week usually, as we do some internal testing first. Some of these changes then get backported to stable after testing, which then gets released ~1-2 weeks later too.

We're hoping to release v5 beta as a stable release soon (weeks?) after we improve performance a bit more. If you pin your prod to the current latest beta release after testing it in preview/staging for a bit, it's unlikely you'll have any negative surprises.